There are a variety of different types of faults that may affect an electronic system. In general, faults may be classified as systematic faults or random faults. A systematic fault is one that occurs as a result of a manufacturing defect. A systematic fault, for example, may be a defect, e.g., a “bug,” in electronic hardware and/or in software. Systematic faults may be addressed through implementation of best practices including a variety of checks performed throughout development and manufacturing of the electronic system.
A random fault is one that may occur due to aging of the electronic system, environmental conditions, or the like. Two examples of random faults include “Single Event Upsets” (SEUs) and “stuck-at faults.” An SEU is a condition where a circuit element changes state as a result of a charged particle impacting at or near a transistor junction. The collision of the charged particle with the junction can induce an upset to the state of the transistor. In the case of a memory cell, the change in state is a bit flip where the value of a bit stored in the memory cell changes from a 0 to a 1 or from a 1 to a 0.
A stuck-at fault is a type of defect where application of a particular signal value or values to a circuit results in a logical error. For example, a stuck-at 1 fault is where a particular signal is expected to take on a value of 0 given a particular set of input values to the circuit, but instead takes on a value of 1. A stuck-at 0 fault is where a particular signal is expected to take on a value of 1 given a particular set of input values to the circuit, but instead takes on a value of 0.
The occurrence of a random fault, whether an SEU and/or a stuck-at fault, within an electronic system may result in a system failure. As such, detection of random faults is an important aspect of electronic system design. This is particularly true in the case of devices and/or systems that are considered to be “fail-safe.” A fail-safe device or system is one that, in the event of a failure, is able to respond in a way that will not cause harm or, in the alternative, cause only a minimum amount of harm, to other devices or personnel.